Tributyltin esters and antifouling compositions comprising the same



United States Patent 3,211,680 TRIBUTYLTIN ESTERS AND ANTIFOULING COMPOSITIONS COMPRISING THE SAME David M. Updegraff, North Oaks, and Horace R. Davis,

Roseville, Minn., assignors to Minnesota Mining and.

Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Filed Sept. 18, 1961, Ser. No. 138,576

9 Claims. (Cl. 260-19) This invention relates to compositions adapted to the prevention of marine fouling, and particularly to paints for structures immersed in sea water.

The problem of the fouling of marine structures has been recognized for many years (cf. Protective and Decorative Coatings, I. J. Mattiello, vol. III, Chapter 12B, John Wiley and Sons, Inc., New York, 1943). Stationary structures such as piers, wharves and the like become encrusted with organisms below the Water line and are unsightly. The problem with moving structures such as boats and barges of all types is more serious since not only are they made unsightly by the algal growth which occurs near the water line, but, of even greater significance, the extensive growth on the submerged part of the hull results in increased resistance to movement through the water and a consequent waste of power. Furthermore, the calcareous shells of the barnacles may case breakage of the protective paint film and open the way for corrosion of metal hulls or invasion of wooden hulls by one or more of the numerous marine borers which abound in some waters and Weaken wooden structures. This latter problem furthermore extends to stationary structures and is exacerbated by the difficulty of cleaning such structures at regular intervals; which can be done for vessels by drydocking, scraping and repainting. It is Well recognized that fouling in its broad sense is a serious problem which leads to economic loss throughout the world.

Prior art compositions have suffered from the fact that most such compositions, while they are eventually toxic to the fouling organism's, do not wholly prevent the attachment of the cypris larvae. This is the stage in the development of the larva of the barnacle at which it is capable of attachment. As a result, the barnacle grows for a greater or lesser time and then dies, leaving a calcareous plate attached to the submerged structure. This provides a roughened surface which increases friction in water and serves as a secondary base for further attachment of organisms, which are at least to some extent protected from the anti-fouling paint thereby. Thus, although many prior art compositions have shown useful inhibition of fouling, they have not fully prevented it. It is also a characteristic of the prior art paints, nearly all of which contain cuprous oxide, that they have a dark color, which prevents their being manufactured in aesthetically pleasing lighter hues. Furthermore, these paints (i.e., those which are copperor cuprous oxide-based) aggravate the corrosion of steel-hulls and the corrosion products counteract their antifouling activity.

'It is, therefore, an object of the present invention to provide a novel class of tributyltin oxide esters which, when mixed into suitable film forming vehicles, form marine antifouling compositions which, in addition to 3,211,680 Patented Oct. 12, 1965 preventing the fouling of submerged structures for extended periods of time, may be prepared in the lighter colors and do not aggravate the corrosion of steel hulls. It is another object of this invention to provide a method for the prevention of fouling of marine structures. A further object is to provide compositions for application to marine structures to prevent fouling. Other objects will become evident to those skilled in the art by reading the specification which follows.

In accordance with these and other objects of the invention, it has been found that when not less than about ten percent by Weight of a member of the class consisting of tributyltin toluenesulfonate, tributyltin isonicotinate, bis(tributyltin) terephthalate and tetrakis(tributyltin) pyromellitate is dispersed in a substantially waterinsoluble film forming vehicle (such, for example as spar varnish, vinyl acetate-vinyl chloride copolymer base paints, and the like), marine anti'foul-ing paint composition-s are formed which are capable of providing essentially complete protection to submerged structures from marine fouling for extended periods of time. (The term tributyltin toluene sulfonate as used herein includes the tributyltin esters of the ortho-, metaand para-toluenesulfonic acid isomers and mixtures thereof.) Thus panels coated with antifouling paints comprising these novel compositions of matter and exposed to severe fouling conditions in the ocean near Miami, Florida, remain free of fouling for periods of several months. Under comparable conditions, untreated control panels become heavily encrusted with barnacles.

Preferably these antifouling paints contain from about 25 to 85 percent by Weight based on the dry paint film or about 10 to 50 percent by weight based on the liquid paint composition of a tributyltin ester according to the invention. Antifouling paints containing amounts of the esters below this range are relatively ineffectual in inhibiting the growth of marine antifouling organisms while those containing amounts in excess thereof are unsatisfactory with regard to their film-forming properties (e.g., such films often lack the requisite cohesive and adhesive properties for antifouling paints). It is noted that the action of the tributyltin esters in the antifouling paints of the invention may be either as repellents, as toxicants or both and the occasional use herein of the term tox icants with respect thereto is for purposes of convenience rather than limitation in this regard.

Tributyltin toluenesulfonate, tributyltin isonicotinate, bis(tributyltin) terephthalate and tetrakis(tributyltin) pyromellitate, are prepared by condensing bis tributyltin oxide with toluenesulfonic acid, isonicotinic acid, terephthalic acid and pyromellitic acid, respectively, and removing the water formed in the reactions. They may be either added to paint formulations as crystalline materials which readily disperse in the vehicle or melted and poured with agitation into the vehicle. In the preparation of the toluenesulfonate, it is often preferable to use the easily available and relatively inexpensive commercial toluenesulfonic acid in the preparation of the esters of the invention. Typically this acid has the following specifications: toluenesulfonic acids, 94% (a mixture of about para isomer and 20% ortho isomer); sulfuric acid, 1.0% max.; water, 2.0% max.; andstoluene, 0.2% max.

The toxicants may be utilized in various antifouling paint vehicles including exfoliating or submerged chalking types, in which the surface is deliberately loaded with inert fillers to control the water permeability of the film and promote chalking (e.g., see Young, G. H., Schneider, W. K., and Scagren, G. W., Industrial and Engineering Chemistry, 36, 113-1132, 1944); cannon ball or particle contact types in which a high concentration of toxicant is used in a relatively water impermeable and insoluble matrix and the toxicant is made available largely by slow dissolution out of the matrix structure (e.g., see Ferry, J. D., and Ketchum, B. H., Industrial and Engineering Chemistry, 38, 806-810, August 1946); and soluble matrix types in which the matrix slowly dissolves thus releasing the toxicant (e.g., see Ketchum, B. H., Ferry, J. D., and Burns, A. E., Industrial and Engineering Chemistry, 38, 931-936, September 1946); and modifications of each of these. The vehicles of all marine antifouling paints may be considered to be permeable since a degree of permeability is necessary to make the active'ingredients initially available at the surface of the paint film. In the particle contact type of paint, however, vehicles which are relatively insoluble in sea water may be used since the major mechanism for making the active ingredients available is through the exposing of new particles of active ingredients by the dissolution of other particles thereof with which they are in contact.

Conventional additives for antifouling paint compositions such as fillers, driers, thickeners, pigments, dyes and the like can, if desired, be added to the antifouling paint compositions of the invention, so long as the toxicant concentration is above the minimum effective concentration and the permeability of the particular base is not adversely afiected. Similarly, agents Which tend to increase the water permeability of antifouling paint films, e.g., rosin, may be added. The addition of such agents and the consequent increase of the permeability of the antifouling paint films will, other things being equl, result in a relatively more rapid release of toxicant and consequently a shorter period of protection from entifouling.

The paint-like compositions of the invention are applied by brushing, spraying, rolling or by other convenient methods to form the final coating for surfaces exposed to fouling. They can be applied over other paint if desired. Thus, application of one or more priming and corrosion-resisting coatings may be followed by one or more coatings of the compositions of the invention. In making the application, the normal procedures of cleaning and priming the surfaces are carried out and the antifouling coating is applied last. Two or more coatings may be applied if desired but this is generally not necessary if thorough coverage of the surface is effected with one coat.

The following examples will illustrate the best mode contemplated for practicing the invention without being limiting thereto, since it is within the skill of the art to prepare further formulations consisting of paint vehicles incorporating the esters as herein defined, following the disclosure herein made. All parts are by weight unless otherwise specified.

Example] .-Preparation of tributyltin p-t o luenesulfonate A beaker containing 298 grams of bis tributyltin oxide and 190 grams of p-toluenesulfonic acid monohydrates is heated for 3 hours at 140 C. The contents of the beaker are then poured into a mortar and allowed to cool and the resulting hard crystalline material is ground with a pestle to a fine powder. This material is found to melt at 85-89 C. and to contain 50.0 parts of carbon and 7.4 parts of hydrogen compared to calculated values of 49.5 percent and 7.4 percent respectively for tributyltin toluenesulfonate.

Example 2.Preparati0n of tributyltin isonicotinale A solution of 24.6 grams of isonicotinic acid and 59.6 grams of bis tributyltin oxide in 300' cc. of toluene is refluxed in a reaction flask fitted with a condenser and a Barrett trap which serves to remove the water of reaction as it is formed. When approximately the theoretical amount of water has been removed from the reaction mixture, the pressure in the flask is reduced and a part of the solvent is removed in order to precipitate the tributyltin isonicotinate. The resulting white solid precipitate is recovered in 78 percent of the theoretical yield from the clear solution by filtration and drying. It is found to melt at 136-137 C. and to contain 52.7 percent of carbon, 7.4 percent of hydrogen, 3.4 percent of nitrogen and 28.6 percent of tin compared to caluclated values of 52.5 percent, 7.6 percent, 3.4 percent and 28.8 percent, respectively.

Example 3.Preparation of bis(tributyltin)terephthalate A mixture of 8.6 grams of terephthalic acid and 30.7 grams of his tributyltin oxide is heated in an open reaction vessel for 1 hour at 200 C. and is then poured into a mortar and allowed to cool. The resulting hard crystalline solid is ground into a fine powder and is found to weigh 36.1 grams (94 percent of the theoretical amount). This product, which melts te -82 C. contains 51.3 percent of carbon and 8.1 percent of hydrogen as compared to calculated values of 51.6 percent and 7.9 percent, respectively.

Example 4.Preparati0n. of tetrakis(tributyltin) pyromellitate A mixture of 25.4 grams of pyromelli-tic acid and 119.7 grams of his tributyltin oxide is heated in an open meaction vessel for 3 hours at 140 C. and then tfior 6 hours at 200 C. The resulting molten product is poured into a mortar and allowed to cool. The resulting hard crystalline mass is ground to a fine powder which weighs 1 30.4 grams (92.5 percent of theoretical yield). The melting point of this product is 93-95 C. and it is found to contain 49.2 percent of carbon and 8.1 percent of hydrogen compared to calculated values of 49.3 percent and 7.9 percent, respectively.

Example 5 A number of antifiouling paint compositions are prepared by mixing the finely divide-d tributyltin esters into a marine spar varnish having the following approximate composition:

Parts by weight For purposes of comparison, similar mixtures are also prepared utilizing bis tributyltin oxide and cuprous oxide (a commercially available antifouling agent) as toxicants.

Panels of exterior type plywood are coated with each of the paint mixtures and a contnol panel is coated'with' the same paint base to which no toxicant has been added. The panels :are exposed to 'fiouling conditions by submerging them in the sea at Miami, Florida, and are examined monthly to determine the ability of each to retain at least percent :antifouling activity. The 85' percent antifioul mg activity is determined as follows: The number of barna-cles, hydroids, bryozoa, oysters, tubeworms, and. other macroscopic fouling .organisms which adhere to; ea-ch test panel is counted once each month, and com-- pared with the number of the same types of organisms on a non-toxic plate glass panel of the same area immersed for the same period. The percent antifouling activity is then calculated utilizing the following equation:

Percent antifouling activity =100- where x is the number of fouling organisms on the test panel and y is the number of fouling organisms on the non-toxic control panel. The results are set out in the following table, in which the concentrations of the respective toxicants are given both as percentages of the total paint compositions applied to the panels and as percentages of the resulting dry paint films.

Example: 6

The novel compositions of the invention are also evaluated as toxicants for antifouling paints using as a vehicle a 13 percent solution of VYHH vinyl chloride-vinyl acetate copolymer in a solvent consisting of 60 parts by weight of methylisobutylket-one and 40 parts of xylene. The results of anti fioulling tests run in the manner previously described in the sea at Miami, Florida on panels coated with these formulations (and with the test vehicle containing no toxicant) are given in the following table, the number of months which the panels retain at least 85 percent antifouling activity being reported.

An antifouling paint based on the same copolymer solution vehicle and containing 25 percent (on wet weight basis) of tributyltin toluenesulfonate, prepared by reacting bis tributyltin oxide with technical gnade toluenesulfonic acid (containing about 76 percent of p-toluenesulionic acid and 1 9 percent of o-toluenesulfonic acid together with small amounts of water, sulfuric acid, toluene, etc.) protects wooden panels from marine fouling for several months (i.e., the coated test panels retain at least 8 5 percent antifouling activity over the period of months when tested in the manner previously described).

Example 7 Modified soluble matrix type paints are prepared by mixing the novel compositions of the invention into the following vinyl-base coating (which meets U.S. Navy 6 specifications for US. Navy antifouling paint formula No. 121):

Parts by weight Vinyl chloride-vinyl acetate copolymer 1 Gum rosin 80 Tricresyl phosphate 30 Methyl isobutyl ketone 275 Xylene 1 1 A copolymer of 87 mole percent vinyl chloride and 13 mole percent vinyl acetate.

This formulation, which is white in color, may be pigmented to provide a standard grey color. A number of antifouling paints according to the invention are prepared by adding varying amounts of the toxicants to the formulation. Test panels of exterior type plywood are then coated with each of these paints and are tested for resistance to fouling according to the procedure of the previous example. The results are given in the following table:

Percent Concentration of Toxieant Toxicant Months Wet Dry Basis Basis Tributyltin p-toluenesulfonate 20 46 2 50 78 18 'Iributyltin isonicotinate 33 63 11 20 46 5 50 78 7 Bis (tributyltin) terephthalate 33 63 14 20 46 13 Tetrakis (tributyltin) pyromellitate The terms and expressions which have been employed are used as terms of description and not of limitation, and it is not intended, in the use of such terms and expressions, to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. An ester of bis tributyltin oxide selected from the class consisting of tributylin toluenesulfonate, tributyltin isonicotinate and tetrakis(tributyltin) pyromellitate.

2. Tributylin toluenesulfonate.

3. Tributyltin isonicotinate.

4. Tetrakis(tributyltin) pyromellitate.

5. A marine antifouling composition comprising, in admixture, a permeable marine paint containing from about 25 to 85 weight percent based on the dry paint film of an ester of his tributyltin oxide selected from the class consisting of tributyltin toluenesulfonate, tributylin isonicotinate, bis (tributyltin) terephthalate and tetrakis (tributyltin) pyromellitate.

6. An antifouling composition as in claim 5 wherein the active ingredient is tributyltin toluenesulfonate.

7. An antifouling composition as in claim 5 wherein the active ingredient is tributyltin isonicotinate.

8. An antifouling composition as in claim 5 wherein the active ingredient is bis(tributyltin)terephthalate.

9. An antifouling composition as in claim 5 wherein the active ingredient is tetrakis(tributyltin) pyromellitate.

References Cited by the Examiner UNITED STATES PATENTS 2,727,917 12/55 Mack et al. 260-429] 3,095,434 6/63 Stamm et a1. 260429.7

FOREIGN PATENTS 578,312 6/46 Great Britain. 846,687 8/ 60 Great Britain.

LEON J. BERCOVITZ, Primary Examiner.

MILTON STERMAN, Examiner. 

1. AN ESTER OF BIS TRIBUTYLIN OXIDE SELECTED FROM THE CLASS CONSISTING OF TRIBUTYLIN TOLUENESULFONATE, TRIBUTYLTIN ISONICOTINATE AND TETRAKIS(TRIBUTYLTIN) PYROMELLITATE.
 5. A MARINE ANTIFOULING COMPOSITION COMPRISING, IN ADMIXTURE, A PERMEABLE MARINE PAINE CONTAINING FROM ABOUT 25 TO 85 WEIGHT PERCENT BASED ON THE DRY PAINT FILM OF AN ESTER OF BIS TRIBUTYLIN OXIDE SELECTED FROM THE CLASS CONSISTING OF TRIBUTYLTIN TOLUENESUFONAT, TRIBUTYLIN ISONICOTINATE, BIS (TRIBUTYLTIN) TEREPHTHALATE AND TETRAKIS (TRIBUTYLTIN) PYROMELLITATE. 